What would SNP demand in return?
Nothing of benefit to UK obviously.

Scotland is the UK just as much as Hertfordshire is the UK. As is the Westcountry, Wales and Northern Ireland. Politicians fighting their own corners is the inevitable consequence of our horribly south-east-centric way of running the country. Boris fights his corner very well for London, right? Do you think he does it with altruistic intention for the rest of the UK? If it's OK for Boris, why isn't it OK for Alex?